ColorImagingText.tioga
Maureen Stone, July 22, 1987 10:21:21 pm PDT
Color Imaging and Reproduction
Color Production
Color Reproduction
Color Measurement
Calibrated Color Reproduction
What is Color?
Red, Green, Yellow, ...
Hue, Tone, Tint ...
Response of Eye to Stimulus
Perception of Stimulus
Anything Not a Mask
Color Devices
Device Characteristics
Additive or Subtractive
Bilevel or Multilevel
Monitors (Additive)
Printers (Subtractive)
Color Monitors
Red, Green, Blue Primaries
Three Phosphor Dots/Pixel
Multilevel
Full Color
Color Lookup Tables
40 spi to 100 spi
Color Printers
Three or Four Color
Cyan, Magenta, Yellow
Above Plus Black
CMY, CMYK
Bilevel or Multilevel
150 to 2500 spi
Digital Color Printing
Bilevel Technologies
Inkjet
Electrostatic
Xerography
Thermal Transfer
Offset Printing
Multilevel Technologies
Photographic Processes
Thermal Sublimation
Halftone Patterns
Pattern of Variable Sized Dots
Halftone Screen
Originally Mechanical
50 to 200 lines/inch
Different Rotations
Trade Spatial Resolution for Grayscale
Digital Halftones
Multiple Printer Pixels/Dot
Gray Levels vs. Sharp Edges
10:1 typical
10 by 10 = 101 gray levels
150 lines = 1500 spi
Digital Color Printers
Poor Resolution
Good Alignment
Designing Colors on Monitors for Printers
Additive vs. Subtractive Color
Different Viewing Environments
User Model
Functional Color
Select Percentage CMYK
RGB to CMY(K) Automatically
Color Reproduction
Goal
Same Image
Different Output Devices
Same Appearance
Graphic Arts Rules-of-Thumb
Customer Satisfaction
Color Names Don't Change
Gray Scale is Smooth and Gray
Good Contrast
Gray Scale Production
Monitors
R=G=B is Gray
Gamma Correction
Linear in Intensity
Printers
C=M=Y is Not Gray
Gray Balancing
Linear in Density
Density = Log[1/R]
RGB to CMY(K)
If Inks were Ideal Filters
[C,M,Y] = [1,1,1] - [R, G, B]
Inks are Not Ideal Filters
Spectra Overlap
Not Inverse of Monitor Spectra
Color Correction Required
Color Correction
Map Input to Output Colors
Compensate
For Color Impurity
For Color of Primaries
Different Gamuts
Techniques
Single Linear Transformation
Piecewise Interpolation
Color Measurement
Measure What the Eye Sees
Colorimetry
Instruments Measure the Stimulus
Empirically Derived
Metrics Standardized by the CIE
Device Calibration
Define Device Properties
in Colorimetric Terms
Model or Measure
Set of All Possible Colors Defines Gamut
Calibrated Color Reproduction
Color Correction Based on Colorimetric Information
Calibrated Devices
Possible Reproduction Levels
Match Surfaces
Match Tristimulus Values
Match Chromaticity Coordinates
Match Appearance
AIC Experiment
Color in Computer Generated Displays
AIC Interim Meeting, 19-20 June 1986
Color Research and Application
Vol. 11, Supplement, June 1986
John Wiley and Sons, NY, NY
With John Beatty and William Cowan
What We Learned
Goal is Appearance Match
Map to Control Appearance
Map to Control Out-of-Gamut Colors
Don't Match Exact
Tristimulus Values
Chromaticity Coordinates
Conclusions
Increasing Number of Digital Color Devices
Many are Poor Quality
Many are Badly Used
Color Reproduction Important Issue for Computer Graphics Community
Color Measurement Key to Quality Reproduction